1. Field of the Invention
The invention concerns a process for securing a flat strip lamella to a surface of a building component, the lamella comprising a plurality of carbon fibers extending parallel to each other in the lamella longitudinal direction and embedded in a binder matrix, wherein a face of the flat strip lamella is pressed against a surface of a building to which an adhesive layer of a reaction resin had been applied in a paste-like consistency, and wherein the adhesive layer is hardened to form an adhesive bond or joint.
2. Description of the Related Art
Flat strip lamellas of this type are used for strengthening of load-bearing or load-transmitting building or construction components. They are conventionally adhered to a construction component surface using an adhesive layer of an epoxy resin. In this process, it has often been found to be a disadvantage that the hardening of the adhesive requires a relatively long period of time, during which the construction component being re-enforced or the building structure cannot be subjected to loads.
Beginning therewith, it is the task of the present invention to improve the process of the above-described type in such a manner that, with a relatively simple means, a significant acceleration of the hardening process can be achieved.
Advantageous embodiments and further developments of the invention can be seen from the dependent claims.
The inventive solution is based on the idea that the adhesive layer, which is comprised of a reaction resin, hardens faster as the temperature of the adhesive is increased. In order to achieve this, it is proposed in accordance with the invention that an electric current is conducted through a part of the carbon fibers, heating the re-enforcing lamella and thereby heating the adhesive layer via the re-enforcing lamella, herein advantages taken of the fact that the carbon fibers extending through the entire length of the flat strip lamella have a certain electrical conductivity, which can be used for an ohmic heating of the flat strip lamella.
According to a preferred embodiment of the invention, the adhesive layer is heated to a temperature of  greater than  40xc2x0 C. via the re-enforcing lamella. Thereby, the curing or hardening time required for, e.g., an epoxy resin adhesive, which at environmental temperature may require approximately 1-2 days, can be reduced to 1-2 hours. Further, the hardening at higher temperatures results in a higher glass transition point and a better stiffness and bonding effect of the adhesive.
For introduction of the electrical current, one metallic contact plate connected to a source of current is preferably pressed against each of the respective ends of the flat strip lamella. In certain cases it is necessary to reduce the transmission resistance between the contact plate and the lamella surface. For this purpose, prior to the application of the contact plates, the lamella upper surface at the contact point can be roughened up or ground down, exposing of carbon fibers.
In accordance with one preferred embodiment of the invention, the temperature can be measured over time at least one position on the re-enforcing lamella and/or the adhesive layer, and by variation of the current supply the electrical heat yield can be adjusted or regulated in accordance with a predetermined protocol.
In order to obtain reproducible heating times, it is recommended in accordance with the invention to measure the electrical resistance of the flat strip lamella extending between the metallic contact plates prior to the heating process, and to adjust the electrical voltage and/or the current strength at the current source in accordance with a predetermined surface-area dependent power density taking into consideration the measured resistance.